A Cellulose fiber is a substance having a basic skeleton of all the plants, is accumulated on the earth in an amount exceeding one trillion tons, and is a resource that is renewable by planting trees, and therefore effective utilization thereof is desired. Although the weight is one fifth of that of steel, the cellulose fiber has strength five times stronger than steel and a low linear thermal expansion coefficient as low as 1/50 of glass fiber. Thus, a technology in which cellulose fiber is contained as a filler in a matrix of a resin or the like to impart mechanical strength to the resin is proposed (Patent Literature 1). Moreover, in order to further improve the mechanical strength of a cellulose fiber, there is a proposal on a fibrous resin reinforcing agent in which the cellulose fiber is defibrated so that a cellulose nanofiber (CNF or microfibrillated plant fiber) may be present in a dispersed state in an additive (Patent Literature 2). Furthermore, as a material obtained by subjecting a cellulose fiber to defibration treatment in the same manner as in producing the CNF, a cellulose nanocrystal (CNC) is known. The CNF is a fiber that is obtained by subjecting a cellulose fiber to defibration treatment such as mechanical defibration and that has a fiber width of about 4 to about 100 nm and a fiber length of about 5 μm or more. The CNC is a crystal that is obtained by subjecting a cellulose fiber to chemical treatment such as acid hydrolysis and that has a crystal width of about 10 to about 50 nm and a crystal length of about 500 nm. These CNF and CNC are collectively called as nanocellulose. Nanocellulose has a high specific surface area (250 to 300 m2/g) and has a lighter weight and a higher strength when compared with steel.
The thermal deformation of nanocellulose is smaller when compared with that of glass. Nanocellulose having a high strength and a low thermal expansion is a useful material as a sustainable type resource material, and creation and development of, for example, a composite material achieving a high strength and a low thermal expansion by combination of nanocellulose and a polymer material such as a resin; an aerogel material; an optically anisotropic material making use of a chiral nematic liquid crystal phase formed by self-organization of CNC; and a high-functional material obtained by introducing a functional group into nanocellulose have been made. On the other hand, nanocellulose plentifully has hydroxy groups and therefore is hydrophilic and strongly polar, which makes nanocellulose inferior in compatibility with general purpose resins that are hydrophobic and nonpolar. Therefore, in the material development using nanocellulose, studies have been conducted on improving the compatibility of nanocellulose with general purpose resins by modifying the surface of nanocellulose or introducing a functional group into nanocellulose through chemical treatment. That is to say, studies on improving dispersibility of nanocellulose to general purpose resins have been conducted.
Moreover, in the preparation of a general purpose resin composition containing a cellulose fiber as a filler, studies have been conducted on improving the dispersibility and compatibility of a cellulose fiber with general purpose resins by adding a dispersant. In Non Patent Literature 1, the dispersibility of a cellulose nanocrystal (cellulose nanowhisker) inorganic solvents is improved by adsorbing a surface active agent to the cellulose nanocrystal. In Non Patent Literature 2, an isotactic polypropylene (iPP) composite material is prepared using, as a reinforcing material, a cellulose nanocrystal to which a surface active agent is adsorbed and the tensile strength of the composite material is improved about 1.4 times stronger than that of the iPP alone. In Patent Literature 2, when cellulose is utilized as a reinforcing material for a thermoplastic resin, an additive (low-molecular weight surface active agent) having affinity to a cellulose fiber and having a particular HLB (hydrophile-lipidophile balance) value is used to create a state in which the cellulose fiber is dispersed in the additive for the purpose of suppressing the occurrence of cellulose aggregates and uniformly dispersing cellulose in a resin.